Modify Power supply for Tube Amp

gnometto · 4th February 2012, 03:21 PM

Hello , i need help to modify the voltage from 1st schematic and adapt to the 2nd . Please HELP ME ! B1 are 320v , B2 310v
Thank you

riccoryder · 4th February 2012, 05:53 PM

Which transformer do you have (center tap? Voltages?)? That is very important. You could get double the voltage if you use the first transformer in the second circuit without a few simple but essential changes. Capacitors could fail, spit and smoke, or even explode.

gnometto · 5th February 2012, 06:07 PM

The trasformer is center tap 330v-0-330v rectified from tube 5Z3P and measured on B1 320v and B2 310v . I will build the 2nd schematic and i have all of the 1st schematic , how i can reduce the voltage to B1 278v and B2 260v , what i must change ?
Thanks

boywonder · 10:29 PM

PSUDII is your friend here.....

PSUD2

Is your transformer 290-0-290 or 330-0-330? Are you measuring 330-0-330 unloaded? Do you know the inductance & DCR of the choke (or can you measure it?) How much current are the EL34, 6N9P and 12AU7 pulling in both schematics? Do you know (or can you measure) the DCR of the transformer secondary?

With the above info, you can model the existing PS (I just did for fun and got pretty close to your 320 B1 and 310 B2) and characterize the transformer pretty close and then modify for the second schematic.

riccoryder · 5th February 2012, 11:02 PM

There is no need to reduce the voltage. The numbers on the diagram are just typical voltages to expect, not maximums. That circuit will be perfectly happy with the higher voltage. Based on the cathode resistor and cathode voltage, you're within the power rating for the tube, and otherwise that tube is rated for 800 Volts. When a tube data sheet shows typical values, like for class A, those are not maximums either. The important thing is not to exceed the dissipation rating (too much heat), and too much current through the output transformer can saturate the core. The driver is fine too, each tube is operating at a fairly low voltage. The filament voltages should be close to the rated 6.3 Volts, running up to 10% lower helps tube life, higher shortens it. I estimated the currents by dividing the voltage in the cathode circuits by the resistance. Then that current multiplied by supply voltage is input power to that section - just under 1.1 Watts total for the input tubes, and around 21 for the output (that's both plate and screen, plate alone will be even lower)

gnometto · 7th February 2012, 10:35 AM

riccoryder , you thihk i can leave the ps from the 1st circuit for the 2nd ??? for el34 is ok , for the 12au7 is not too much volts ?

5th February 2012, 10:14 PM	#4
boywonder diyAudio Member Join Date: Jan 2008 Location: So.Cal.	PSUDII is your friend here..... PSUD2 Is your transformer 290-0-290 or 330-0-330? Are you measuring 330-0-330 unloaded? Do you know the inductance & DCR of the choke (or can you measure it?) How much current are the EL34, 6N9P and 12AU7 pulling in both schematics? Do you know (or can you measure) the DCR of the transformer secondary? With the above info, you can model the existing PS (I just did for fun and got pretty close to your 320 B1 and 310 B2) and characterize the transformer pretty close and then modify for the second schematic. Last edited by boywonder; 5th February 2012 at 10:29 PM.

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4th February 2012, 05:53 PM	#2
riccoryder diyAudio Member Join Date: Dec 2011	Which transformer do you have (center tap? Voltages?)? That is very important. You could get double the voltage if you use the first transformer in the second circuit without a few simple but essential changes. Capacitors could fail, spit and smoke, or even explode.

5th February 2012, 06:07 PM	#3
gnometto diyAudio Member Join Date: Nov 2011	The trasformer is center tap 330v-0-330v rectified from tube 5Z3P and measured on B1 320v and B2 310v . I will build the 2nd schematic and i have all of the 1st schematic , how i can reduce the voltage to B1 278v and B2 260v , what i must change ? Thanks

5th February 2012, 11:02 PM	#5
riccoryder diyAudio Member Join Date: Dec 2011	There is no need to reduce the voltage. The numbers on the diagram are just typical voltages to expect, not maximums. That circuit will be perfectly happy with the higher voltage. Based on the cathode resistor and cathode voltage, you're within the power rating for the tube, and otherwise that tube is rated for 800 Volts. When a tube data sheet shows typical values, like for class A, those are not maximums either. The important thing is not to exceed the dissipation rating (too much heat), and too much current through the output transformer can saturate the core. The driver is fine too, each tube is operating at a fairly low voltage. The filament voltages should be close to the rated 6.3 Volts, running up to 10% lower helps tube life, higher shortens it. I estimated the currents by dividing the voltage in the cathode circuits by the resistance. Then that current multiplied by supply voltage is input power to that section - just under 1.1 Watts total for the input tubes, and around 21 for the output (that's both plate and screen, plate alone will be even lower)

7th February 2012, 10:35 AM	#6
gnometto diyAudio Member Join Date: Nov 2011	riccoryder , you thihk i can leave the ps from the 1st circuit for the 2nd ??? for el34 is ok , for the 12au7 is not too much volts ?

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